This invention relates to tubular grinding mills such as ball or rod mills wherein a tubular mill shell having an inlet for course material to be ground and an outlet for finely ground material has grinding media such as balls or rods within the shell whereby as the mill shell is rotated about its own axis the grinding media is tumbled within the mill shell to comminute the material. Mills of this type are typically used in the grinding of cement raw meal, cement clinker or the grinding of ores. More particularly, the present invention relates to a division head for use in such a grinding mill for dividing the mill into compartments.
Typically, a grinding mill of the type in which the present invention is utilized will include various size grinding balls within the mill with the larger balls being in the upstream or inlet side of the mill and the smaller balls being in the downstream or outlet side of the mill. A division head may be utilized within the head to divide the mill into compartments. In a given compartment there may be various size grinding balls but as a general statement, the larger balls are in the first or upstream compartment and the smaller balls are in the second or downstream compartment. The larger balls serve to reduce the size of the course incoming feed to a smaller size to thereby achieve a first size reduction. The smaller balls are used to achieve a second, final size reduction in the downstream compartment.
Material flow through a grinding mill depends upon both size reduction and displacement of material. The flow is dependent upon size reduction in that at either the discharge from a compartment or the discharge from the mill, grates are provided which have openings sufficiently large to permit the passage of material of a given size but sufficiently small to prevent both the grinding media and oversize material to be ground from passing from one compartment either into the next compartment or out of the ball mill. The flow of material through the mill is also governed by displacement in that as material is fed into the mill a substantially equal amount of material is discharged from the mill.
It is desireable to control the level of material within a given compartment of the mill in order to have adequate material within the mill to retain the material within a compartment or the mill long enough to achieve proper size reduction. In addition, since the material being ground which is dispersed between the grinding media acts as a cushion and lubricant to thereby reduce the wear rate on the grinding balls and the mill liners, maintaining a desired level of material within the mill serves to prolong the life of the grinding media.
Prior to the present invention it was known to provide a means for controlling the flow of material from one compartment of a tubular grinding mill to a second compartment of that tubular grinding mill or to the discharge of the mill. Two such devices are shown in U. S. Pat. Nos. 3,801,025 and 4,171,102 both of which utilize a means defining a reservoir of material within a partition in the mill and a scoop arrangement for picking up material from that reservoir and feeding it through a central discharge into the next compartment or to the outlet of the mill. A further device for controlling the flow of material through a mill is illustrated in U.S. Pat. No. 3,633,832.